Flat wedge-shaped lens and image processing method

ABSTRACT

A flat lens system includes a wedge-shaped refractive material having a first surface and a second surface opposite to the first surface for refracting incident light beams from an object having a width of Y, from the first surface towards the second surface; a reflective material positioned at the second surface of the wedge-shaped refractive material for reflecting the refracted light beams at a first angle toward the first surface, wherein the reflected light beams are refracted from the first surface at a second angle to form an image of the object having a width of X and including chromatic aberrations; and an apparatus for processing the image of the object to reduce said chromatic aberrations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/222,058, filed on Jul. 28, 2016, which claims the benefitsof U.S. Provisional Patent Application No. 62/201,428, filed on Aug. 5,2015, and the entire contents of which are hereby expressly incorporatedby reference.

FIELD OF THE INVENTION

The disclosed invention generally relates to a flat lens system andcorrecting aberrations of images from the flat lens system usingconfiguration and image processing techniques.

BACKGROUND

Anamorphic prism systems are known to compress or expand light beams,but they have not been used for image capture for a variety of reasons.These prism systems are afocal, and do not focus an image onto an imageplane, making them unsuitable as an imaging system. Typically,anamorphic prism systems are designed for collimated light from oneincident angle and therefore their performance degrades with off axislight, resulting in a lens with a very limited field of view. Manyanamorphic prisms have chromatic dispersion resulting in chromaticaberrations making them unsuitable for multi-color images. Accordingly,anamorphic prism systems are almost exclusively used to shape laserbeams, often monochromatic, and are generally referred to as beamexpanders and beam compressors.

Achromatic anamorphic prism systems, generally require multiple prismsmaking them large and heavy. In addition, since the achromaticanamorphic prism systems only compress or expand in one dimension, itwould require multiple of these systems to compress equally in twodimensions to maintain the image aspect ratio, which makes the systemseven larger and heavier. For these reasons anamorphic prism systems havenot been used for image capture.

Imaging devices such as cameras, microscopes and telescopes can be heavyand large. A large portion of this weight is due to the design of theoptical lens elements, which can include heavy curved lenses, and thestructure to support these lens separated by long focal distances. Theseimaging devices can be large (thick) mainly because in a typical lenssystem, the opening aperture to system device depth ratio is small.Moreover, to optically improve image resolution with the traditionallens systems, more device depth (longer focal length) is required inorder to reduce lens refraction and minimize lens aberrations. Thedevice depth of the imaging device can limit the imaging systems'performance and design. For example, the size and weight constraints ofmobile, compact, or weight constrained imaging devices can limitresolution because they constrain the maximum focal length. Thedisclosed invention can increase the effective focal length in thesesystems, and improve resolution with the same size and weightconstraints.

Additionally, conventional curved lenses have many different types ofaberrations that reduce image resolution (spherical, coma, chromatic,and others). To correct these aberrations, conventional curved lensesuse extra large pieces of precision glass, adding weight, size and costto the lens system. The disclosed invention can reduce the size, weightand resulting cost of conventional curved lenses, and in some deviceseliminate their use entirely.

SUMMARY OF THE INVENTION

In some embodiments, the disclosed invention is a flat lens system whichincludes: a wedge-shaped refractive material having a first surface anda second surface opposite to the first surface for refracting incidentlight beams from an object having a width of Y, from the first surfacetowards the second surface; a reflective material positioned at thesecond surface of the wedge-shaped refractive material for reflectingthe refracted light beams at a first angle toward the first surface,wherein the reflected light beams are refracted from the first surfaceat a second angle to compress or expand the light from the object havinga width of X and including chromatic aberrations; and an apparatus forforming and processing the image of the object to reduce said chromaticaberrations.

In some embodiments, X is smaller than Y to compress the image of theobject for use in a telescope, for instance. In some embodiments, X islarger than Y to expand the image of the object for use in a microscope,for example.

In some embodiments, the reflective material may include one or moremoving or rotating mirrors to reflect the refracted light beams atvarying angles toward the first surface.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosed invention, and many of theattendant features and aspects thereof, will become more readilyapparent as the disclosed invention becomes better understood byreference to the following detailed description when considered inconjunction with the accompanying drawings in which like referencesymbols indicate like components.

FIG. 1 shows a comparison of a tradition circular curved lens with aflat (wedge) lens, according to some embodiments of the disclosedinvention.

FIG. 2 shows an exemplary configuration of a flat lens system, accordingto some embodiments of the disclosed invention.

FIG. 2A illustrates a wedge-shaped refractive material, according tosome embodiments of the disclosed invention.

FIG. 3 is an exemplary process flow, according to some embodiments ofthe disclosed invention.

FIG. 4 depicts an exemplary flat (wedge) lens with a moving reflectivesurface, such as one or more moving mirrors, according to someembodiments of the disclosed invention.

FIG. 5 shows an exemplary flat lens for expanding EM waves, according tosome embodiments of the disclosed invention.

DETAILED DESCRIPTION

Embodiments of the disclosed invention are directed to a flat lenssystem to obtain a high quality image with a more compact optical lenssystem and correcting aberrations of images from the flat lens systemusing configuration and image processing techniques. Increasing theinitial surface area of the lens objective (aperture) allows moreelectromagnetic (EM) wave energy to be collected, and can result in afaster and better image quality. However, increasing the aperture toimprove image quality and speed typically results in a proportionallylarger size lens system and device depth.

The flat lens system according to the disclosed invention has anincreased initial surface area of the lens objective (aperture), with adecreased corresponding device depth in the lens stack. The flat lenssystem collects the EM waves, such as visible and nonvisible lights,with a much larger aperture-to-device depth ratio. This means higherquality images can be captured faster with a smaller device depth. Aflat lens system may be very large for telescopes for example, and smallfor microscopes, and yet maintain a large aperture-to-device depthratio.

FIG. 1 shows a comparison of a tradition circular curved lens with aflat (wedge) lens, according to some embodiments of the disclosedinvention. The figure shows how a flat lens system with a square lightsensor can collect twice as much light as a conventional lens systemwith circular lens, and a square light sensor. As shown, the area 106 ofthe rectangular light sensor is 2r², while the area 104 of the circularlens is πr², which is larger. The area 102 is 2r by 2r=4r². As seen, aflat (wedge) lens system captures twice the light in a device with asimilar frontal area, and therefore can take higher quality images anddo so in a faster manner. This ratio would be even larger forrectangular sensors, which most sensors are.

In some embodiments, the disclosed invention provides a flat lens systemand image processing methods with an increased lens aperture to devicedepth ratio and corrects aberrations and distortions in the imagesproduced by the lens. In some embodiments, the disclosed invention iscapable of optical EM wave compression and/or expansion. Someapplications for the flat (wedge) lens of the disclosed inventioninclude both imaging and non-imaging applications. Examples of imagingapplications are cameras, microscopes, telescopes, binoculars, scopes,telecentric lenses, and the like. Examples of non-imaging applicationsare architectural light pipes, which could provide indoor illuminationusing natural light, and solar concentrators for more efficient solarenergy generation.

FIG. 2 shows an exemplary configuration of a flat lens system, accordingto some embodiments of the disclosed invention. A wedge shapedrefractive material 202 with angles a1 and a2 is formed on top of areflective surface 204 to form a flat lens. The image of an object 201with a width of Y is reflected from multiple surfaces of the flat(wedge) lens, processed and compressed to form a compressed image 218 ofthe same object. As shown, light (EM) waves 206 a and 208 a at the twoends of object 201 are penetrated into the refractive material 202 andreflected from the reflective surface 204 at an angle to form lightwaves 206 b and 208 b, respectively. The reflected lights (EM) 206 b and208 b are further reflected from the internal surface of the refractivematerial 202 to form light waves 206 c and 208 c, respectively. Theangle of the light waves 206 c (a4) and 208 c (a3) leaving therefractive material can be designed for specific applications, usingconventional optical design methods. Reflected light waves 206 c and 208c now form a smaller size X (compressed) image 210 of the originalobject 201.

Varying angles a1 and/or a2 will vary the size X of the compressed image210. The size X of compressed image 210 varies with the EM wavelength,angle a1 and a2, and the type of the refractive material 202. Angles a1and/or a2 values can be varied for specific applications, such as thedegree of the compression (X) needed. In many typical applications,angles a1 is between 15 and 25 degrees and a2 is between 75 to 105degrees. Exit beam angles of a3 and a4 can be modified by varying anglesa1 and/or a2 until the critical angle is reached which then alters thebeam path to total internal reflection.

Referring back to FIG. 2, the compressed image is then directed to anoptional focusing lens 212 to focus the compressed image onto lightsensor(s) 214 (for example, CCD or CMOS sensor(s)). In some embodiments,the focusing lens 212 focuses the compressed image onto an eyepiece forviewing by a human. An image processor 216 (implemented in software,hardware and/or firmware) corrects for any aberrations resulting fromthe lens system by using one or more image processing techniques. Anexample of correcting chromatic aberrations in hardware would be the useof one or more optical wedges and/or diffraction gratings, before thelight sensor 214, that together have an achromatic effect for imaging.The refractive properties of the material of the wedge 202 can bechanged to assist in controlling chromatic dispersion for imagingapplications as well. For example, the refractive index of the wedge canbe dynamically changed by applying voltage to current to the wedgecomprised of certain material that refract the light differently underelectric power.

If the image processing is performed by an optical device (hardware),the correction is done before the image is received by the sensor.However, if the image processing is performed by software (executed on aprocessor), the corrections are performed after the image is received bythe image sensor, that is, at the output of the sensor.

In some embodiments, the chromatic dispersion for the output image isdynamically measured (for example, at predetermined intervals) and acorresponding voltage (or current) is applied to the wedge to change itsrefractive index and/or its beam absorption to compensate for themeasured chromatic dispersion. In some embodiments, the amount of thevoltage (or current) applied to the wedge is determined from a storedlookup table, taking into account the measured chromatic dispersion andthe type of the wedge material.

Characterizing the chromatic dispersion per device, and applyingsoftware algorithms in the image processor 216 to the image, can also beused to assist in controlling chromatic dispersion for imaging

There are many known image processing techniques to correct for imageaberrations. One method is to calculate or measure the aberrations ofthe system, for example, by creating spot diagrams, which are differentfor each wavelength of light, and then apply an inverse transferfunction to reverse these aberrations.

The refractive material 202 may be made of any type of glass, plastic,fluids such as water, or similar types of refractive materials. In caseof a fluid, such as water, the fluid may also be used to allow coolingof the optics. The reflective surface 204 may be any type of mirror orother material having a reflective surface. Such reflective surface maybe attached or coated on such material to form the reflective surface204.

The flat lens of the disclosed invention may have any rectangular shape,rather than a square shape, which allows for variable compression ratioand aspect ratio of the image being formed. In some embodiments, thewedge angles a1 and a2 can be variable as the specific applicationsrequire. For example, using common BK7 glass, a typical wedge angle a2may vary between 75 and 105 degrees, in some embodiments. Choosing anangle a2 closer to 75 degrees will result in higher energy captured andlower chromatic aberration but have lower compression. However, choosingan angle a2 closer to 105 degrees results in a higher compression of theimage at the expense of higher energy losses and larger chromaticaberration. Angle a1 can be varied to produce similar effects.

Although FIG. 2 and its description is directed to visible light and animage, those skilled in the art would recognize that the flat lens ofthe disclosed invention is not limited to visible light. Rather, thedisclosed invention is capable of operating on any type of EM wave thatcan refract, with or without forming an image.

FIG. 2A illustrates a wedge-shaped refractive material (prism),according to some embodiments of the disclosed invention. As shown areflective material is coated or attached to the back of thewedge-shaped refractive material. The wedge-shaped prism has a vertexangle α (e.g., between 2 and 25 deg.). If one surface of the prism isreflectorized (by the reflective material), a thin anamorphic beamexpander/compressor can be created. In this case, it is shown that theoutput beam is orthogonal to the input beam. Although FIG. 2A,illustrates a reflecting wedge anamorphic compressor prism that convertsan input beam with an aspect ratio of, for example, 2:1 to an outputbeam with an aspect ratio of, for example, 4:3, one skilled in the artwould recognize that any prism designed for anamorphic compression canbe used as an expander by reversing the direction of the input and viceversa. The ray-trace equations of the prism are

$\begin{matrix}{{{I\; 1} = \varphi},} & (1) \\{{I_{1}^{\prime} = {\arcsin \left( \frac{\sin \; I_{1}}{n} \right)}},} & (2) \\{{I_{2} = {{\alpha + I_{1}^{\prime}} = I_{2}^{\prime}}},} & (3) \\{{I_{3} = {I_{2} + I_{2}^{\prime} + I_{1} - I_{1}^{\prime} - \varphi}},} & (4) \\{{I_{3}^{\prime} = {\arcsin \left( {n\; \sin \; I_{3}} \right)}},} & (5) \\{\delta = {\varphi + {I_{3}^{\prime}.}}} & (6)\end{matrix}$

Here, α≅(I₃−I₁′)/2 and φ is the tilt angle of surface 1 from thevertical. φ and α may be adjusted until the desired compression orexpansion ratio is obtained. For instance, for a prism of B270 opticalcrown glass (n_(d)=1.5229) with φ=16.9 deg and α=14.0 deg, an anamorphiccompression A′/A=MAG≈0.375 can be obtained. Typically, two of thesereflective wedges, placed orthogonally to maintain the image aspectratio, would result in a shortening the focal length required of thefocusing lens system by 50% or more. This effect may be used to create amore compact device.

Compressing the image using this technique allows the image to befocused in a shorter distance while maintaining resolution. A shorterfocal distance allows for a more compact device. This means higherquality images can be captured faster with a smaller lens system. FIG. 3is an exemplary process flow, according to some embodiments of thedisclosed invention. In block 302, an EM energy (which may or may notcontain an image) enters an optical system comprising one or more flat(wedge) lens. The EM energy goes through the medium and bounces off areflective surface, in block 304. In this example, it is assumed thatthe EM wave is visible light forming an image. However, as explainedabove, the disclosed invention is not limited to visible light andimages, rather, it is applicable to any EM wave/energy. The reflected EMwave then travels through the medium and exits the optical elements, inblock 306, where the EM wave will be compressed or expanded in one ormore plane(s). In block 308, the EM wave may then travel through anoptional modifying (focusing and correcting) lens system. In block 310,the EM wave strikes one or more EM sensor(s) or optical element(s) forhuman eye viewing. Block 302 to block 308 may be repeated multiple timesto compress the EM Wave in multiple planes. In the case of imaging, thecompressed output aperture from 306 reduces the required focal lengthwhich reduces the corresponding device size. In block 312, a processor,such as an image or EM wave processor, receives the information from theEM sensor and modifies/enhances this information, as required by theapplication of the flat lens. This can also be used to expand/spread theimage if the application is directed to a microscopic function, wherethe sequence is partially reversed.

In block 314, in the case of imagery application, the (image) processorcorrects aberrations from the lens system. The refracting wedge lens canintroduce chromatic aberrations, but does not introduce otheraberrations usually associated with circular lens systems. The chromaticaberration can be predetermined (by calculation or measurement) for eachpixel. A table can be used to offset each color at each pixel toreposition the pixel at the appropriate position in the resolved image.

Alternatively, or in combination, hardware (optical) processing of theimage may be performed by achromatic elements, such as achromaticwedge(s). An anamorphic prism for correcting an anisotropy of aradiation angle of a beam is described in U.S. Pat. No. 4,750,819, theentire contents of which is hereby expressly incorporated by reference.The anamorphic prism is formed as an achromatic structure using a firstprism and a second prism. The refractive indexes and refractive indexchanges as a result of a wavelength fluctuation of the first and secondprisms and an incident angle of the beam to the first prism can satisfya predetermined relationship, where the beam can emerge from the secondprism at an exit angle of 0 degree, which corrects the anisotropy of theangle of the beam.

The flat lens system of the disclosed invention collects the EM waves,such as visible and/or non-visible light, with a much largeraperture-to-device depth ratio. This means higher quality images can becaptured faster with a smaller lens system.

The flat lens system may be very large for telescopes for example, andsmall for microscopes, and yet maintain a large aperture-to-device depthratio. The image sensors are often charge coupled devices (CCDs) or CMOSsensors. The disclosed invention is not limited to the above examples ofimaging sensor, rather, other types of EM or imaging sensors may be usedwith the flat lens of the disclosed invention. Human eye viewableoptical elements may also be used. In the case of human eye viewableoptical elements, blocks 308 to 314 may not be required because thehuman eye can focus the image.

In block 312, one or more processor(s), such as an image or EM waveprocessor(s), receives the information from the EM sensor(s) andmodifies/enhances this information, as required by the application. Thiscan also be used to expand/spread the image if the application isdirected to a microscopic function, where the sequence is partiallyreversed.

In the case of a three dimensional (3D) imaging, more EM sensors may berequired, as known in the art. The invention is not limited to the aboveexamples of imaging sensor, rather, other types of EM or imaging sensorsmay be used with the flat lens of the disclosed invention.

FIG. 4 depicts an exemplary flat (wedge) lens with a moving reflectivesurface, such as one or more moving mirrors, according to someembodiments of the disclosed invention. As shown, the image of an object401 is reflected from multiple surfaces of the flat (wedge) lens,processed and compressed to form a compressed image 414 of the sameobject. Light (EM) waves at the two ends of object 401 are penetratedinto the refractive material 402 and reflected from moving mirrors 404at varying angles to form a smaller size (compressed) image 406 of theoriginal object 401.

The compressed image 406 may optionally get directed to an optionalfocusing lens 408 to focus the compressed image onto light sensor(s) 410(for example, CCD or CMOS sensor(s)). An image processor 412(implemented in software, hardware and/or firmware) corrects for anyaberrations resulting from the lens system by using one or more imageprocessing techniques and output a corrected compressed image 414. Ifthe image processing is performed by an optical device (hardware), thecorrection is done before the image is received by the sensor. However,if the image processing is performed by software (executed on aprocessor), the corrections are performed after the image is received bythe image sensor, that is, at the output of the sensor.

In these lens systems with moving reflective surface, the quality of theimage is increased by reducing the field of view, and stitching manyimages together. This technique can improve final image resolution.Moving the mirror changes the view of what objects appear in the image.In these embodiments, the mirror is moved in a way that it can capturesa series of images, each with a narrow field of view. The system thenuses known image processing techniques to combine or stitch the capturedimages together into one composite image with a large field of view. Forexample, known image stitching methods may be used to register,calibrate and blend the images to produce the final image 414. Becausethe imaging system has a relatively large aperture size with lots oflight, images can be captured very quickly. Another reason to move themirror is to adjust the field of view, or change the compression of onesingle image, for example, for digital or optical zooming applications.

There are several different techniques to move the mirror 404. Althoughmirror 404 is shown as rotating, in some embodiments, it is possible totilt the reflective surface (e.g., a mirror) about a fulcrum, or rotateabout the edge as shown in FIG. 5. In some embodiments, the mirror canbe an array of micromirrors. The moving reflective surface(s) of theflat lens system may be combined with the dynamic changing of therefractive index of the refractive wedge-shaped material (as describedabove) to further enhance the lens system.

FIG. 5 shows an exemplary flat lens for expanding EM waves, according tosome embodiments of the disclosed invention. FIG. 5 described below,illustrates a microscopic function, where the EM paths are reversed withrespect to those depicted in the example of FIG. 2. Light leaves a smallsize (X) object 502, and enters a wedge 504 where it is expanded, andreflected off a reflective surface 506, such as a mirror. The light thenexits the wedge into a lens system 510, light sensor 512, and imageprocessor 514. The processed image is an expanded image 516 of the smallsize image 502. Further expanding the expanded image 516, for example,by varying the angle a1 and/or a2 and/or a3 and/or configuring multiplewedges in series to further expand the small object image 502, thefunction of a microscope can be realized with a much smaller deviceand/or enable higher resolution and/or viewable area. In someembodiments, the wedge may include an anti-reflective coating(s) tocapture more of the light energy leaving the small object. Similar toflat lens systems of FIG. 4, if the image processing is performed by anoptical device (hardware), the correction is done before the image isreceived by the sensor(s). However, if the image processing is performedby software (executed on a processor), the corrections are performedafter the image is received by the image sensor(s), that is, at theoutput of the sensor(s).

There are several known image processing methods to correct the imageaberration caused by the flat lens. The use of these known methods isdependent upon the application of the flat lens. For example, lookuptables may be used to correct the aberrations as a relatively simplecorrection for chromatic aberrations. Moreover, transfer functions maybe appropriated when fixing chromatic aberrations in a flat lensapplication.

In some applications, there may be a low intensity of EM energy, such asin low light applications (e.g., night vision, or for example RamanSpectroscopy of biological tissue where high power lasers may damage thetissues). In these applications, the large aperture of the lens systemof the disclosed invention is capable of collecting a large amount oflight energy, and still use a very compact design.

In some embodiments, the disclosed invention is capable of capturing andoptionally process multispectral or hyperspectral imaging, which is usedto collect and process information from across the electromagneticspectrum to obtain the spectrum for each pixel in an image of a scene,with the purpose of finding objects, identifying materials, or detectingprocesses in the image of the scene.

In some embodiments, the disclosed invention is scalable and applies toa full range of system sizes including those from small microscopic/nanosystems to large telescopic systems greater than, for example, 30 m islength or diameter.

It will be recognized by those skilled in the art that variousmodifications may be made to the illustrated and other embodiments ofthe invention described above, without departing from the broadinventive scope thereof. It will be understood therefore that theinvention is not limited to the particular embodiments or arrangementsdisclosed, but is rather intended to cover any changes, adaptations ormodifications which are within the scope of the invention as defined bythe appended claims and drawings.

1. A flat lens system comprising: a wedge-shaped refractive materialhaving a first surface and a second surface for refracting incidentlight beams from an object from the first surface towards the secondsurface, the incident light beams having a width of Y; and a reflectivematerial positioned at the second surface of the wedge-shaped refractivematerial for reflecting the refracted light beams at a first angletoward the first surface, wherein the reflected light beams arerefracted from the first surface at a second angle and having a width ofX to be used to form an image of the object.
 2. The flat lens system ofclaim 1, wherein X is smaller than Y to compress the image of theobject.
 3. The flat lens system of claim 1, wherein X is larger than Yto expand the image of the object.
 4. The flat lens system of claim 1,further comprising a focusing lens to focus the image of the object ontoa sensor.
 5. The flat lens system of claim 1, further comprising afocusing lens to focus the image of the object onto an eyepiece forviewing by a human.
 6. The flat lens system of claim 1, furthercomprising an apparatus for processing the image of the object to reducechromatic aberrations of the image of the object.
 7. The flat lenssystem of claim 6, wherein the apparatus for processing the image is animage processing device executing an image processing programming codeto reduce said chromatic aberrations.
 8. The flat lens system of claim6, wherein the apparatus for processing the image comprises of one ormore refractive optical wedges that together have an achromatic effectto reduce said chromatic aberrations.
 9. The flat lens system of claim6, wherein the apparatus for processing the image comprises of one ormore diffraction gratings that together have an achromatic effect toreduce said chromatic aberrations.
 10. The flat lens system of claim 1,wherein the refractive or reflective material has one or more coatingsat the first or the second surface.
 11. The flat lens system of claim 1,wherein the reflective material is attached to the second surface of thewedge-shaped refractive material.
 12. The flat lens system of claim 1,wherein the reflective material comprises of one or more moving mirrorsto reflect the refracted light beams at varying angles toward the firstsurface.
 13. The flat lens system of claim 11, wherein the one or moremoving mirrors are rotated or tilted to reflect the refracted lightbeams at varying angles.
 14. The flat lens system of claim 1, furthercomprising an electric energy source electrically coupled to thewedge-shaped refractive material to dynamically change a refractiveindex of the refractive material to refract the incident light beams atvarying angles.
 15. The flat lens system of claim 1, further comprisingone or more wedge-shaped refractive material(s) positioned between thewedge-shaped refractive material and the reflective material.
 16. Atelescope comprising the flat lens system of claim
 1. 17. A microscopecomprising the flat lens system of claim
 1. 18. A binocular comprisingthe flat lens system of claim
 1. 19. A scope comprising the flat lenssystem of claim
 1. 20. A telecentric lens system comprising the flatlens system of claim 1.